Orangutans share 97 per cent of their DNA with humans and can live to the age of 40. Research leader Dr Alex Weiss said : “Such research across a wide range of species could yield fascinating insights into the evolutionary basis of happiness . ”

Professor Richard Byrne, a primate expert from the University of St Andrews , said: “The team has worked out that the difference between an orangutan being rated as very happy, compared to very unhappy, equated to 11 additional years of life expectancy.”